One of my goals for SNES Central is to investigate the origins of ROM images of prototypes that have leaked out over the years. I think from NSRT, there are several hundred games listed as "BETA", with no qualifier. I'm sure many of these originate from scene releases, and in many cases are hacked. Anyways, first I am focusing on unreleased games, and I will post the results here.

Dorque & Imp - The ROM images of three demos, posted directly by the developers. These are assembled binaries, rather than being something ripped from a cart.

Iron Commando (PAL version) - Originally released by Paradox in December 1994, with an intro hacked in. The version floating around now is almost certainly hacked to remove the intro, so I would not regard it as being a clean dump.

Corn Buster - The binary was posted by the developer on their website, I would regard this as being a clean dump.

Pinkie - Posted on Unseen64 a couple of years ago. Although they did not elaborate on the origin, I would suspect that the original developer gave them the assembled binary, and this was not ripped from a cart.

Mick & Mack - Global Gladiators - Scene release by Sabotage, though I do not have an exact date. The trainer screen (which I think was a legitimate thing used by the developer) has been hacked by the scene group. The version floating around has subsequently been hacked to remove the BBS phone number.

Quik the Thunder Rabbit - leaked a few weeks ago on Assembler Games. The person who leaked it hacked in a title screen in a bid to obscure the person who gave the ROM to him. I would even argue that Quik the Thunder Rabbit might not necessarily be the title of the game (which is unknown), since this is likely a sequel of the original Amiga game.

Speedy Gonzales (PAL version) - I dumped this myself, I hope you can trust me.